Material for conversion to cellulose derivatives and process of producing same



atented Mar. 29, 1932 GEORGE A. RICHTER, MILTON O. SCHUR, AND ROYAL H. RASCH, OF BERLIN, NEW HAMPSHIRE, ASSIGNORS T BROWN COMPANY, OF "BERLIN, NEW HAMPSHIRE, A

CORPORATION OF MAINE MATERIAL FOR CONVERSION TO GELLTI'LOSE DERIVATIVES AND PROCESS OF JPBODUGING SMZIE ale Drawing.

lhis invention relates to the preparation of cellulose derivatives from cellulosic material, and has for its object to provide a process of conditioning such material to improve its characteristics for conversion into the cellulose derivatives, such, for example, a as those lower nitrocelluloses customarily used as a base in the manufacture of nitrocellulose products such as lacquers, films, artificial silk,

celluloid, and the like.

The cellulosic material herein conditioned is a chemical wood pulp, preferably one containing a high percentage of alpha or resistant cellulose and herein reterred'to as high alpha cellulose fiber. Such high alpha cellulose fiber may be converted into cellulose derivatives having physical and chemical properties comparable to those prepared from cotton fiber or cotton linters, in contrast to the relatively impure derivatives having interior properties prepared from chemical wood fiber of lower alpha cellulose content. The high alpha cellulose fiber may be produced as described in application for patent, Serial No. 72,522, filed December 1, 1925, by George A. Richter andMilton O. Schur, by treating a raw or unbleached fiber, e. g, sulphite pulp, containing. say, about 85% to 87% alpha cellulose, under proper temperature conditions, in a solution of caustic soda or equivalent alkaline agents of suitable concentration. During such treatment, certain nonalpha cellulose constituents present in the fiber, such as the beta and gamma cellulose and ligncous and coloring material, are dissolved, so that atter the requisite period of treatment there results a refined or purified fiber containing upward of 93% alpha cellulose. The refined fiber requires a relatively small amount of bleach for conversion into a fiber of high whiteness, usable as a new rag or cotton fiber substitute in the manufacture of bond; ledger and writing papers of the finest quality and in the preparation of cellulose derivatives of high commercial value and squeezing.

Application filed. October 9, 1928. Serial Ito. 140,677.

purity. It may be desirable, especially if the raw fiber contains a percentage of non-alpha constituents higher than usual, to pretreat the fiber with an oxidizing solution, e. g. a chlorine solution, to remove a portion of such constituents or to facilitate their removal by subsequent treatment in the alkaline solution.

If a fiber of very high alpha cellulose content, say, 95% to 98%, is desired, the alkaline treatment may be succeeded by a second alkaline treatment, as described in application for patent, Serial No. 75,888, filed December 16, 1925, by George A. Richter. By a double alkaline treatment, the quantity of bleach required to produce fiber of high whiteness is materially reduced. The refined fiber serves as an excellent rawmaterial for the preparation of cellulose derivatives.

W e have discovered that it cellulose fiber, and more particularly a refined wood fiber such as hereinbefore described-which for convenience of designation will be termed alpha cellulose wood fiber,is conditioned for nitration by mercerization in a solution of caustic soda, the nitrating characteristics of such fiber are markedly improved.

For instance, the fiber may be fiufied Ine chanically to resemble cotton linters from a thick sheet formed on a cylinder machine from a very dilute suspension of pulp, and dried on the mould, either with or without The alpha fiber in fiufied condition may, for example, be steeped in a caustic sodasolution of 17.5%, or greater, strength, at C. for minutes, followed successively by a washing with cold water, a souringwith 20% acetic acid solution and a final washing with hot water. The product may then be dried and nitrated into the lower nitrocelluloses, with mixed acids of suitable strength.

Mercerization efiects a change in the character of the fiber, which upon nitration asserts itself in a lower acid retention and a higher yield of nitrocellulose product. Acid [iii stronger films and other products may be formed than from solutions produced from 'unmercerized fiber. One factor contributing to these results doubtless is that during mercerization a further removal of non-alpha cellulose constituents in the alpha fiber is effected, and hence there results a purer nitrocellulose, from which better lacquers, films or plastics may be produced.

The superior product, as well as the higher ield and lower acid retention, may also e imputed to the change in physical characteristics which mercerization effects on the fiber. Our observation is that a change in the structure of the fiber which retards the action of the mixed nitrating acids improves the purity and quality of the product, raises the yield, and lowers the acid retention. This observation is borne out by the fact that an increase of couching pressure before drying, in sheeting the alpha fiber on a paper machine, produces noteworthy advanta es in nitration. Or, if the web of alpha her is filled with, say, 1% or more of nitrocellulose or regenerated cellulose as described and claimed-in our companion application, Serial No. 140,676, filed concurrently herewith, ad-

vantages in nitration are observable. These results are further in accord with the disclosure in our application for patent, Serial No. 97,998, filed March 27, 1926, wherein it 'is set forth that beating or hydration of the fiber prior to nitration is accompanied by fayorable results. Mercerization appears to effect results somewhat similar to beating, and, if desired, may be combined with a beat- 1 ing of the fiber, so that the advantages incilow yield and high acid retention.

.the pulp is mercerized,-however, the initial dent to both may be realized.

Our further conclusion is that, when the pulp is highly absorptive, it is attacked rapidly by the sulphuric acid present in the mixed nitrating acid, partly dissolving or forming esters therewith, which arehydrolyzed and dissolved during subsequent washing of the product, necessarily resulting in a When attack by the sulphuric acid is modified and the nitric acid is allowed time to penetrate into the fibers in the proper concentration-to form stable nitrates. I

By lowering the reactivity of the cellulosic material, we also decrease the chance for local overheating in the nitrating acid bath.

retrace cerized by the treatment set forth in the example, an increase in yield from 126 .to 141, a lowering of the acid retention from about 8 to 5.5, a decrease in the viscosity of the solu tion of nitrocellulose product and a marked improvement inthe color of the solution were noted.

The mercerizing treatment may, ofcourse,

be varied. Thus, the'time of mercerization may be'five minutes or less, and the washing after mercerization may be done with hot wa-v ter, or the temperature of mercerization may be varied. For example, noteworthy improvements have been realized by steeping fiufi'ed high alpha pulp two to three minutes in a 7% caustic solution at 10 C. The fibers in this case rapidly assume a gelatinized condition,

but are easily separated from the caustic soda after the addition of a large volume of hot water. The results attained upon nitration, in any event, however, indicate a slight increase in yield, a material lowering of the acid retention, and a marked improvement in color and other characteristics of the nitrated product. Thus, mercerization at a low temperature of flufi'ed high alpha cellulose wood fiber prepared by mechanically disintegrating a dry, spongy sheet made on a cylinder machine, produces upon nitrationan increase in yield from 125 to 145', a decreasein acid retention from 8.4 to 5.3, and a marked improvement in color of the product.

Unmercerized unbeaten chemical wood pulp is very poorly suited for use as raw material in the preparation of the lower nitrates because, among other things, (1) it leads to high wastage of nitrating acid, owing to itshigh acid-retention in the centrifugal; (2)

115 it gives a low yield of nitrocellulose; (3) it linters, and, as above pointed out, gives an,

tion, an expedient, that may be attended by a loss in yield and in nitric acid, and an in- 'crease in the brittleness of the nitrocellulose product. A inercerized chemical wood pulp, on the other hand, produces a low viscosity nitrocellulose even at temperatures slightly below those used in the nitration of cotton increased yield of product of superior physical characteristics.

The best results are obtained when the alpha fiber is both beaten and mercerized. By beating, we mean mechanically hydrating or gelatinizing the fiber in a hollander or other suitable apparatus. Merccrized beaten alpha cellulose wood fiber yields nitrocellulose from which films and other products may be prepared having properties comparable to those-obtained with good grade linters or with a moderately high grade rag sheet. ()ur mercerized fiber conditioned for nitration has, among others, the following charactcristics:

Alpha cellulose content Over Soda solubility amount of fiber dissolved at boiling temperature in 7.14 NaOH solution) Under 10.0 Copper number Under 2.0 Ash Under 0.2 /0 Resins Under 0.25% Pentosans Under 2.0

The present invention thus makes possible the use of a conditioned chemical wood fiber, which may be manufactured at a figure materially lower than that at which cotton linters or cotton are available, for the production of high grade nitrocellulose products.

We are, of course, aware of the fact that mercerization of cellulosic material is in itself broadly old, but, so far as we are aware, the beneficial results obtainable by combining the n'iercerization of wood fiber, and more especially a high alpha cellulose fiber, with nitration, have not heretofore beenrecognized.

0f course, if desired, a certain proportion of cotton linters, cotton, or rag pulp, may be mixed with the alpha fiber. Thus, cotton fiber and the alpha fiber may be mercerized together prior to nitration, or first beaten together, then mercerized, and finally nitrated.

The advantages of the process and the product may be extended to the production of other cellulose derivatives. such as cellulose acetates, for the mercerization of ellulose followed by a hot water treatment as above described will improve materiallv the smoothness oi acetylation and the quality of cellulose acetate obtained, particularlywith regard to the elimination oi undesirable color.

Having thus explained the nature of this invention, it is evident that various changes might be resorted to without departing from the spirit or scope of invention as defined by the appended claims.

'We do not herein claim the subject matter of application Serial No. 77,624, filed December 24, 1925, by George A. Richter, which discloses the mercerizatimi of an unbleached wood fiber, followed by bleaching and conversion into cellulose derivatives; nor do we herein claim generically the subject matter of our companion application Serial No. 140,- 674. filed concurrently herewith and which contains claims generic to the subject matter of that and the present application.

\Vhat we claim is: y

1. A process which comprises mercerizing a bleached high alpha cellulose wood fiber of at least 93% alpha cellulose content, and then converting thc'mercerized fiber into cellulose derivatives.

2. A process which comprises mercerizing a bleached high alpha cellulose wood fiber of at least 93% alpha cellulose content, and then nitrating the mercerized fiber.

3. A process which comprises beating cellulose fiber, mercerizing the same, and then nitrating the mercerized and beaten fiber.

4. A process which comprises treating bleached high alpha cellulose wood fiber with a solution of caustic soda of mercerizing strength, successively washing, acidifying and again washing the treated fiber, drying the fiber, and converting the dried fiber intoa cellulose derivative.

5. A process which comprises treatingbleached high alpha cellulose wood fiber with a solution of caustic soda of mercerizing strength to mercerize the same, washing the mereerized fiber, acidifying and again washing'the fiber, drying the same, and converting the dried fiber into cellulose derivatives.

6. Cellulosic material especially suitable for conversion into nitrocellulose, comprising mercerized high alpha cellulose in a finely shredded condition and substantially free from alkali.

Alpha cellulose content Over 94.5%

Soda solubility (in 7.14 NaOl-l) Under 10.0%

Copper number Under 2.1

9. A cellulose derivative, the cellulose base of which comprises a bleached, mercerized high alpha cellulose wood fiber substantially free from alkali and of at least 93% alpha cellulose content.

4, eemao 10. A nitrocellulose product, the cellulose base of which comprises a beaten and mercerized high alpha cellulose Wood fiber; f

11. Cellulosic material especially suitable for conversion into cellulose derivatives, comprising mcrcerized Wood fiber in a fiufled condition resembling cotton linters. i

12. Cellulosic material especially suitable for conversion into cellulose derivatives, comprising mechanically gelatinized and mercerized Wood fiber in a fluflecl condition resembling cotton linters.

In testimony whereof we have afiixed our signatures.

.GEORGE A. RICHTER. I MILTQN O. SGHUR.

ROYAL H. RASCH. 

